2011 Tohoku Tsunami Runup Distribution and Damages around Yamada Bay, Iwate
Abstract
On 11 March 2011, a magnitude Mw = 9.0 earthquake occurred off the coast of Japan's Tohoku region causing catastrophic damage and loss of life. A month later, distribution of inundation and run-up height for the tsunami was measured in and outside Yamada Bay locating at the middle of Iwate Prefecture. Yamada Bay has a narrow bay-mouth the width of which is approximately 1/4 of the bay width. The bay is surrounded by two peninsulas, Omoe and Funakoshi Peninsulas and locates in the rear of Funakoshi Peninsula for the epicenter. At eastern side of Omoe Peninsula which is exposed to the Pacific Ocean, the average tsunami height was 15 to 20m at the coast line. All villages there had very large run-up heights of more than 25m and houses at lower elevation were almost completely washed away. The highest run-up, around 40m with an inundation distance of 500 m, was measured at Aneyoshi Village. The village locates at the bottom of a small V-shape inlet which concentrates the energy of tsunamis and amplifies their height. Fortunately, the village itself had been moved to higher ground after severe damages brought by Meiji Sanriku (1896) and Showa Sanriku (1933) Tsunamis and had no loss of life by the 2011 Tsunami. At Funakoshi Peninsula, the south east side of which is facing to the epicenter, the average height of incoming tsunami was estimated to be about 15m. On the contrary, tsunami height inside Yamada Bay was much smaller, generally around 6 to 9m. The only exception was the base of Funakoshi Peninsula where tsunami coming from the other side came over the base of Peninsula and caused devastating damage to the area. The exposed areas south of Funakoshi Peninsula like Kirikiri had tsunami run-up of more than 15m. It is considered that the narrow bay-mouth reduced the tsunami height and Funakoshi Peninsula worked as a barrier for Yamada Bay. Yamada Town locating inside Yamada Bay however suffered a large loss of life. The ratio of dead or missing to its population is around 5%, which is high among the cities and towns along the Sanriku Coast. Yamada Town had moderately large lowland areas along the bay and was protected by old and new tsunami seawalls. Height of the old seawall was 4 to 5m, whereas the design height of the new one was 6.6m. For the new seawall, the tsunami height was a little larger but the overflow depth was minimal. There were however old seawalls at some places, which allowed water coming into the town and gave damages to residents' property and life. Considering the height of incoming tsunami, it can be concluded that the damage at Yamada Town was considerably large.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMNH14A..02O
- Keywords:
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- 4564 OCEANOGRAPHY: PHYSICAL / Tsunamis and storm surges